The importance of automatic identification systems increases particularly in the service sector, in the field of logistics, in the field of commerce and in the field of industrial production. Further applications of identification systems are related to the identification of persons and animals.
In particular contactless identification systems like transponder systems (for instance using an RFID tag) are suitable for a wireless transmission of data in a fast manner and without cable connections that may be disturbing. Such systems use the emission and/or absorption of electromagnetic waves, particularly in the high frequency domain (for instance at frequencies of 800 MHz to 900 MHz). Alternatively, such systems may be based on a magnetic coupling (for instance at a frequency of 13.56 MHz).
Such and other systems may use a phase modulated signal of a 13.56 MHz carrier from a reader to a card. Therefore, it is of significance to provide a proper corresponding receiver structure on the label side.
Phase demodulators itself are well known but have to be adapted for specific needs. The need of very high data rates (several Mbit/s) based on a 13.56 MHz carrier may make it necessary to use higher order modulation schemes, and therefore new receiver structures may be necessary as the actual concepts will not be able to handle the needs.
Additionally it is to mention that the receiver structure should be implemented on the card side and therefore the technical effort has to be as low as possible.
FIG. 5 schematically shows a conventional demodulation circuit 500 in which a received signal (phase modulated) 502 is coupled to a mixer 504 for mixing the signal 502 with cos(phi). The mixed signal 506 is supplied to a matched filter unit 508 filtering the signal 506 to generate a signal 510 which is then supplied to a threshold detector 512.
The phase modulated signal 502 received via an antenna can thus be mixed by means of the mixer or multiplier 504 with cos(phi). The received signal 506 is filtered by the filter unit 508. The threshold detector 512 serves for assigning the voltage levels of the, for instance, step-shaped voltage characteristic to different logical states, to thereby reconstruct the information included in the radio signal 502.
However, the demodulator circuit 500 shown in FIG. 5 requires a relatively large space on an integrated circuit and consumes a lot of energy during operation. Furthermore, it may be difficult to detect PSK modulated signals, regarding current and area.